The present invention relates to a ball screw, more particularly, to a ball screw that enables an oil-containing polymer to supply a lubricant automatically for an extended period to a plurality of balls rolling in the helical spaces between the screw shaft and the ball screw nut. Further, the present invention relates to a ball screw which can advantageously be used under severe environments that defy effective lubrication by conventional practices, as exemplified by very hot environments and those where dust particles, corrosive gases, water or other foreign material is present.
FIG. 19 shows a known ball screw which is lubricated with grease or lube oil packed in the spaces 4 between a screw shaft 1 and a ball screw nut 2 which is in threadable engagement with the shaft 1 via a plurality of balls 3. With a view to preventing dust particles and other foreign matter from entering the ball screw nut 2, an annular recess 5 is sometimes formed at each end of the ball screw nut 2, with a seal member 6 being fitted in the recess (to construct a seal-type ball screw).
However, the conventional ball screws which are lubricated with lube oil or grease have a problem that when used in hot environments, the lubricant flows out of the nut 2 to be exhausted so that frequent refilling is necessary.
Further, there is another problem in that if seal members 6 are installed at the ends of the nut 2 with a view to preventing the entrance of dust particles, corrosive gases, water and other foreign matter, friction or wear develops between the screw shaft 1 and each seal member 6, thereby requiring an increased torque to turn the screw.
Examined Japanese Patent Publication (kokoku) Sho. 63-23239 teaches that a paste of a mixture of a superhigh-molecular weight polyethylene and lubricating grease is packed in a ball bearing and melted by heating so that it reaches every part of its interior, followed by cooling to solidify. However, it is not appropriate for this ball bearing lubrication technology to be applied as such to ball screws.